The liberation and metabolism of arachidonic acid (AA) from the cell membrane, results in the generation of pro-inflammatory metabolites by several different pathways. Arguably, the two most important pathways to inflammation are mediated by the enzymes 5-lipoxygenase (5-LO) and cyclooxygenase (COX). These are parallel pathways that result in the generation of leukotrienes and prostaglandins, respectively, which play important roles in the initiation and progression of the inflammatory response. These vasoactive compounds are chemotaxins, which both promote infiltration of inflammatory cells into tissues and serve to prolong the inflammatory response. Consequently, the enzymes responsible for generating these mediators of inflammation have become the targets for many new anti-inflammatory drugs.
Inhibition of the enzyme cyclooxygenase (COX) is the mechanism of action attributed to most nonsteroidal anti-inflammatory drugs (NSAIDS). There are two distinct isoforms of the COX enzyme (COX-1 and COX-2) that share approximately 60% sequence homology, but differ in expression profiles and function. COX-1 is a constitutive form of the enzyme that has been linked to the production of physiologically important prostaglandins, which help regulate normal physiological functions, such as platelet aggregation, protection of cell function in the stomach and maintenance of normal kidney function. (Dannhardt and Kiefer (2001) Eur. J. Med. Chem. 36:109-26). The second isoform, COX-2, is a form of the enzyme that is inducible by pro-inflammatory cytokines, such as interleukin-1β (IL-β) and other growth factors. (Herschmann (1994) Cancer Metastasis Rev. 134:241-56; Xie et al. (1992) Drugs Dev. Res. 25:249-65). This isoform catalyzes the production of prostaglandin E2 (PGE2) from arachidonic acid (AA). Inhibition of COX-2 is responsible for the anti-inflammatory activities of conventional NSAIDs.
Because the mechanism of action of COX-2 inhibitors overlaps with that of most conventional NSAID's, COX-2 inhibitors are used to treat many of the same symptoms, including pain and swelling associated with inflammation in transient conditions and chronic diseases in which inflammation plays a critical role. Transient conditions include treatment of inflammation associated with minor abrasions, sunburn or contact dermatitis, as well as, the relief of pain associated with tension and migraine headaches and menstrual cramps. Applications to chronic conditions include arthritic diseases, such as rheumatoid arthritis and osteoarthritis. Although, rheumatoid arthritis is largely an autoimmune disease and osteoarthritis is caused by the degradation of cartilage in joints, reducing the inflammation associated with each provides a significant increase in the quality of life for those suffering from these diseases. (Wienberg (2001) Immunol. Res. 22:319-41; Wollhiem (2000) Curr. Opin. Rheum. 13:193-201). In addition to rheumatoid arthritis, inflammation is a component of rheumatic diseases in general. Therefore, the use of COX inhibitors has been expanded to include diseases, such as systemic lupus erythromatosus (SLE) (Goebel et al. (1999) Chem. Res. Tox. 12:488-500; Patrono et al. (1985) J. Clin. Invest. 76:1011-1018), as well as, rheumatic skin conditions, such as scleroderma. COX inhibitors are also used for the relief of inflammatory skin conditions that are not of rheumatic origin, such as psoriasis, in which reducing the inflammation resulting from the over production of prostaglandins could provide a direct benefit. (Fogh et al. (1993) Acta Derm Venerologica 73:191-3). Simply stated COX inhibitors are useful for the treatment of symptoms of chronic inflammatory diseases, as well as, the occasional ache and pain resulting from transient inflammation.
In addition to their use as anti-inflammatory agents, another potential role for COX inhibitors is in the treatment of cancer. Over expression of COX-2 has been demonstrated in various human malignancies and inhibitors of COX-2 have been shown to be efficacious in the treatment of animals with skin, breast and bladder tumors. While the mechanism of action is not completely defined, the over expression of COX-2 has been shown to inhibit apoptosis and increase the invasiveness of tumorgenic cell types. (Dempke et al. (2001) J. Can. Res. Clin. Oncol. 127:411-17; Moore and Simmons (2000) Current Med. Chem. 7:1131-44). It is possible that enhanced production of prostaglandins resulting from the over expression of COX-2 promotes cellular proliferation and consequently, increases angiogenesis. (Moore and Simmons (2000) Current Med. Chem. 7:1131-44; Fenton et al. (2001) Am. J. Clin. Oncol. 24:453-57).
There have been a number of clinical studies evaluating COX-2 inhibitors for potential use in the prevention and treatment of different type of cancers. Aspirin, a non-specific NSAID, for example, has been found to reduce the incidence of colorectal cancer by 40-50% (Giovannucci et al. (1995) N Engl J Med. 333:609-614) and mortality by 50% (Smalley et al. (1999) Arch Intern Med. 159:161-166). In 1999, the FDA approved the COX-2 inhibitor CeleCOXib for use in FAP (Familial Ademonatous Polyposis) to reduce colorectal cancer mortality. It is believed that other cancers, with evidence of COX-2 involvement, may be successfully prevented and/or treated with COX-2 inhibitors including, but not limited to esophageal cancer, head and neck cancer, breast cancer, bladder cancer, cervical cancer, prostate cancer, hepatocellular carcinoma and non-small cell lung cancer. (Jaeckel et al. (2001) Arch. Otolarnygol. 127:1253-59; Kirschenbaum et al. (2001) Urology 58:127-31; Dannhardt and Kiefer (2001) Eur. J. Med. Chem. 36:109-26). COX-2 inhibitors may also prove successful in preventing colon cancer in high-risk patients. There is also evidence that COX-2 inhibitors can prevent or even reverse several types of life-threatening cancers. To date, as many as fifty studies show that COX-2 inhibitors can prevent premalignant and malignant tumors in animals, and possibly prevent bladder, esophageal and skin cancers as well.
Recent scientific progress has identified correlations between COX-2 expression, general inflammation and the pathogenesis of Alzheimer's Disease (AD). (Ho et al. (2001) Arch. Neurol. 58:487-92). In animal models, transgenic mice that over express the COX-2 enzyme have neurons that are more susceptible to damage. The National Institute on Aging (NIA) is launching a clinical trial to determine whether NSAIDs can slow the progression of Alzheimer's Disease. Naproxen (a non-selective NSAID) and rofeCOXib (Vioxx, a COX-2 specific selective NSAID) will be evaluated. Previous evidence has indicated inflammation contributes to Alzheimer's Disease. According to the Alzheimer's Association and the NIA, about 4 million people suffer from AD in the U.S.; and this is expected to increase to 14 million by mid-century.
The COX enzyme (also known as prostaglandin H2 synthase) catalyzes two separate reactions. In the first reaction, arachidonic acid is metabolized to form the unstable prostaglandin G2 (PGG2), a cyclooxygenase reaction. In the second reaction, PGG2 is converted to the endoperoxide PGH2, a peroxidase reaction. The short-lived PGH2 non-enzymatically degrades to PGE2. The compounds described herein are the result of a discovery strategy that combined an assay focused on the inhibition of COX-1 and COX-2 peroxidase activity with a chemical dereplication process to identify novel inhibitors of the COX enzymes.
Flavonoids are a widely distributed group of natural products. The intake of flavonoids has been demonstrated to be inversely related to the risk of incident dementia. The mechanism of action, while not known, has been speculated as being due to the anti-oxidative effects of flavonoids. (Commenges et al. (2000) Eur. J. Epidemiol 16:357-363). Polyphenol flavones induce programmed cell death, differentiation, and growth inhibition in transformed colonocytes by acting at the mRNA level on genes including COX-2, Nf kappaB and bcl-X(L). (Wenzel et al. (2000) Cancer Res. 60:3823-3831). It has been reported that the number of hydroxyl groups on the B ring is important in the suppression of COX-2 transcriptional activity. (Mutoh et al. (2000) Jnp. J. Cancer Res. 91:686-691).
Free-B-Ring flavones and flavonols are a specific class of flavonoids, which have no substituent groups on the aromatic B ring, as illustrated by the following general structure:

wherein
R1, R2, R3, R4, and R5 are independently selected from the group consisting of —H, —OH, —SH, OR, —SR, —NH2, —NHR, —NR2, —NR3+X−, a carbon, oxygen, nitrogen or sulfur, glycoside of a single or a combination of multiple sugars including, but not limited to aldopentoses, methyl-aldopentose, aldohexoses, ketohexose and their chemical derivatives thereof;
wherein
R is an alkyl group having between 1-10 carbon atoms; and
X is selected from the group of pharmaceutically acceptable counter anions including, but not limited to hydroxyl, chloride, iodide, sulfate, phosphate, acetate, fluoride, carbonate, etc. Free-B-Ring flavonoids are relatively rare. Out of a total 9396 flavonoids synthesized or isolated from natural sources, only 231 Free-B-Ring flavonoids are known. (The Combined Chemical Dictionary, Chapman & Hall/CRC, Version 5:1 Jun. 2001).
The Chinese medicinal plant, Scutellaria baicalensis contains significant amounts of Free-B-Ring flavonoids, including baicalein, baicalin, wogonin and baicalenoside. Traditionally, this plant has been used to treat a number of conditions including clearing away heat, purging fire, dampness-warm and summer fever syndromes; polydipsia resulting from high fever; carbuncle, sores and other pyogenic skin infections; upper respiratory infections, such as acute tonsillitis, laryngopharyngitis and scarlet fever; viral hepatitis; nephritis; pelvitis; dysentery; hematemesis and epistaxis. This plant has also traditionally been used to prevent miscarriage. (See Encyclopedia of Chinese Traditional Medicine, ShangHai Science and Technology Press, ShangHai, China, 1998). Clinically Scutellaria is now used to treat conditions such as pediatric pneumonia, pediatric bacterial diarrhea, viral hepatitis, acute gallbladder inflammation, hypertension, topical acute inflammation, resulting from cuts and surgery, bronchial asthma and upper respiratory infections (Encyclopedian of Chinese Traditional Medicine, ShangHai Science and Technology Press, ShangHai, China, 1998). The pharmacological efficacy of Scutellaria roots for treating bronchial asthma is reportedly related to the presence of Free-B-Ring flavonoids and their suppression of eotaxin associated recruitment of eosinophils. (Nakajima et al. (2001) Planta Med. 67(2):132-135).
Free-B-Ring flavonoids have been reported to have diverse biological activity. For example, galangin (3,5,7-trihydroxyflavone) acts as anti-oxidant and free radical scavenger and is believed to be a promising candidate for anti-genotoxicity and cancer chemoprevention. (Heo et al. (2001) Mutat. Res. 488(2):135-150). It is an inhibitor of tyrosinase monophenolase (Kubo et al. (2000) Bioorg. Med. Chem. 8(7):1749-1755), an inhibitor of rabbit heart carbonyl reductase (Imamura et al. (2000) J. Biochem. 127(4):653-658), has antimicrobial activity (Afolayan and Meyer (1997) Ethnopharmacol. 57(3):177-181) and antiviral activity (Meyer et al. (1997) J. Ethnopharmacol. 56(2):165-169). Baicalein and galangin, two other Free-B-Ring flavonoids, have antiproliferative activity against human breast cancer cells. (So et al. (1997) Cancer Lett. 112(2):127-133).
Typically, flavonoids have been tested for activity randomly based upon their availability. Occasionally, the requirement of substitution on the B-ring has been emphasized for specific biological activity, such as the B-ring substitution required for high affinity binding to p-glycoprotein (Boumendjel et al. (2001) Bioorg. Med. Chem. Lett. 11(1):75-77); cardiotonic effect (Itoigawa et al. (1999) J. Ethnopharmacol. 65(3): 267-272), protective effect on endothelial cells against linoleic acid hydroperoxide-induced toxicity (Kaneko and Baba (1999) Biosci Biotechnol. Biochem 63(2):323-328), COX-1 inhibitory activity (Wang (2000) Phytomedicine 7:15-19) and prostaglandin endoperoxide synthase (Kalkbrenner et al. (1992) Pharmacology 44(1):1-12). Only a few publications have mentioned the significance of the unsubstituted B ring of the Free-B-Ring flavonoids. One example, is the use of 2-phenyl flavones, which inhibit NAD(P)H quinone acceptor oxidoreductase, as potential anticoagulants. (Chen et al. (2001) Biochem. Pharmacol. 61(11):1417-1427).
The reported mechanism of action related to the anti-inflammatory activity of various Free-B-Ring flavonoids has been controversial. The anti-inflammatory activity of the Free-B-Ring flavonoids, chrysin (Liang et al. (2001) FEBS Lett. 496(1):12-18), wogonin (Chi et al. (2001) Biochem. Pharmacol. 61:1195-1203) and halangin (Raso et al. (2001) Life Sci. 68(8):921-931), has been associated with the suppression of inducible cyclooxygenase and nitric oxide synthase via activation of peroxisome-proliferator activated receptor gamma and influence on degranulation and AA release. (Tordera et al. (1994) Z. Naturforsch [C]49:235-240). It has been reported that oroxylin, baicalein and wogonin inhibit 12-lipoxygenase activity without affecting cyclooxygenase. (You et al. (1999) Arch. Pharm. Res. 22(1):18-24). More recently, the anti-inflammatory activity of wogonin, baicalin and baicalein has been reported as occurring through inhibition of inducible nitric oxide synthase and COX-2 gene expression induced by nitric oxide inhibitors and lipopolysaccharide. (Chen et al. (2001) Biochem. Pharmacol. 61(11):1417-1427). It has also been reported that oroxylin acts via suppression of nuclear factor-kappa B activation. (Chen et al. (2001) Biochem. Pharmacol. 61(11):1417-1427). Finally, wogonin reportedly inhibits inducible PGE2 production in macrophages. (Wakabayashi and Yasui (2000) Eur. J. Pharmacol. 406(3):477-481). Inhibition of the phosphorylation of mitrogen-activated protein kinase and inhibition of Ca2+ ionophore A23187 induced prostaglandin E2 release by baicalein has been reported as the mechanism of anti-inflammatory activity of Scutellariae Radix. (Nakahata et al. (1999) Nippon Yakurigaku Zasshi, 114, Supp. 11:215P-219P; Nakahata et al. (1998) Am. J, Chin Med. 26:311-323). Baicalin from Sculettaria baicalensis, reportedly inhibits superantigenic staphylococcal exotoxins stimulated T-cell proliferation and production of IL-1β, interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ). (Krakauer et al. (2001) FEBS Lett. 500:52-55). Thus, the anti-inflammatory activity of baicalin has been associated with inhibiting the proinflammatory cytokines mediated signaling pathways activated by superantigens. However, it has also been proposed that the anti-inflammatory activity of baicalin is due to the binding of a variety of chemokines, which limits their biological activity. (Li et al. (2000) Immunopharmacology 49:295-306). Recently, the effects of baicalin on adhesion molecule expression induced by thrombin and thrombin receptor agonist peptide (Kimura et al. (2001) Planta Med. 67:331-334), as well as, the inhibition of mitogen-activated protein kinase cascade (MAPK) (Nakahata et al. (1999) Nippon Yakurigaku Zasshi, 114, Supp 11:215P-219P; Nakahata et al. (1998) Am. J. Chin Med. 26:311-323) have been reported. To date there have been no reports that link Free-B-Ring flavonoids with COX-2 inhibitory activity.
To date, a number of naturally occurring Free-B-Ring flavonoids have been commercialized for varying uses. For example, liposome formulations of Scutellaria extracts have been utilized for skin care (U.S. Pat. Nos. 5,643,598; 5,443,983). Baicalin has been used for preventing cancer, due to its inhibitory effects on oncogenes (U.S. Pat. No. 6,290,995). Baicalin and other compounds have been used as antiviral, antibacterial and immunomodulating agents (U.S. Pat. No. 6,083,921) and as natural anti-oxidants (Poland Pub. No. 9,849,256). Chrysin has been used for its anxiety reducing properties (U.S. Pat. No. 5,756,538). Anti-inflammatory flavonoids are used for the control and treatment of anorectal and colonic diseases (U.S. Pat. No. 5,858,371), and inhibition of lipoxygenase (U.S. Pat. No. 6,217,875). Flavonoid esters constitute active ingredients for cosmetic compositions (U.S. Pat. No. 6,235,294).
Japanese Patent No. 63027435, describes the extraction, and enrichment of baicalein and Japanese Patent No. 61050921 describes the purification of baicalin.